Re: [PATCH v3] memcg: fix soft lockup in the OOM process

[Michal Koutný]

Hello.

On Tue, Dec 24, 2024 at 02:52:38AM +0000, Chen Ridong <chenridong@xxxxxxxxxxxxxxx> wrote:
> A soft lockup issue was found in the product with about 56,000 tasks were
> in the OOM cgroup, it was traversing them when the soft lockup was
> triggered.

Why is this softlockup a problem? 
It's lot of tasks afterall and possibly a slow console (given looking
for a victim among the comparable number didn't trigger it).

> To fix this issue, call 'cond_resched' in the 'mem_cgroup_scan_tasks'
> function per 1000 iterations. For global OOM, call
> 'touch_softlockup_watchdog' per 1000 iterations to avoid this issue.

This only hides the issue. It could be similarly fixed by simply
decreasing loglevel= ;-)

cond_resched() in the memcg case may be OK but the arbitrary touch for
global situation may hide possibly useful troubleshooting information.
(Yeah, cond_resched() won't fit inside RCU section as in other global
task iterations.)

0.02€,
Michal

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